1. Field of the Invention
The present invention relates to a display light projection optical device that has characteristics in which display light emitted from a display unit is reflected in the vicinity of one surface and is projected to a predetermined eye point, and external light incident on the other surface is transmitted in a thickness direction.
2. Description of the Related Art
In head-up displays (HUDs) for general vehicles, images of light containing various kinds of information to be displayed are projected from the HUDs to windshields (front window glass) or reflection plates called combiners to form optical paths so that the light reflected from the windshields or the like is oriented in directions of viewpoints of drivers. Accordingly, the drivers can view visual display information of the HUDs shown on the windshields as virtual images simultaneously while viewing scenes in front of the vehicles through the windshields. That is, the drivers can view various kinds of information by display of the HUDs without moving their visual lines while remaining in normal driving states.
PTL 1 discloses that a special optical element (corresponding to the foregoing combiner) is attached on a glass surface of a windshield. Light emitted from an HUD is reflected from the surface of the optical element on the windshield and is oriented in the direction of a viewpoint of a driver. Since the optical element is formed of a material that transmits the visible light, the driver can view not only a display image formed as a virtual image in front of the optical element but also an image of a scene in front of the vehicle in a state in which the image is transmitted through the windshield and the optical element.
PTL 1 discloses that a Fresnel lens is provided on the optical element to form an expansion optical system. Accordingly, the HUD can be miniaturized. Since the Fresnel lens is used, the thickness of the optical element can be decreased.
[PTL 1] JP-A-2012-123393